Mean Circulation in the Great Lakes

In this paper new maps are presented of mean circulation in the Great Lakes, employing long-term current observations from about 100 Great Lakes moorings during the 1960s to 1980s. Knowledge of the mean circulation in the Great Lakes is important for ecological and management issues because it provides an indication of transport pathways of nutrients and contaminants on longer time scales. Based on the availability of data, summer circulation patterns in all of the Great Lakes, winter circulation patterns in all of the Great Lakes except Lake Superior, and annual circulation patterns in Lakes Erie, Michigan, and Ontario were derived. Winter currents are generally stronger than summer currents, and, therefore, annual circulation closely resembles winter circulation. Circulation patterns tend to be cyclonic (counterclockwise) in the larger lakes (Lake Huron, Lake Michigan, and Lake Superior) with increased cyclonic circulation in winter. In the smaller lakes (Lake Erie and Lake Ontario), winter circulation is characterized by a two-gyre circulation pattern. Summer circulation in the smaller lakes is different; predominantly cyclonic in Lake Ontario and anticyclonic in Lake Erie.     

Light-absorbing components in the Great Lakes

Features of light absorption are critical in regulating the optical signal available for remote sensing. The magnitudes, spectral characteristics, spatial patterns, and, to a lesser extent, dynamics of light-absorbing components are documented for the Laurentian Great Lakes. This includes the open waters of each of the five lakes, and selected rivers, embayments and near-shore areas. The absorption coefficient, a(m^? 1), is partitioned according to the additive components (a_x) of colored dissolved organic matter (a_CDOM), non-algal particles (a_NAP), phytoplankton (a_φ), and water itself (a_w; known). Dependencies of a_x on various metrics of optically active constituents (OACs), cross-sections, are evaluated. A wide range of magnitudes of a_x and a, and contributions of a_x to a are documented. For example, the magnitude of a at a wavelength of 440 nm was nearly 10-fold greater in the western basin of Lake Erie than in the open waters of Lake Huron. Rivers, embayments, and near-shore areas generally had higher levels than the open waters. The largest a_x throughout the system was a_CDOM, originating mostly from terrestrial sources. Most of a_NAP was associated with clay mineral particles. The distribution of a_φ was highly correlated to chlorophyll concentration. The collected data set is appropriate to support initiatives to develop and preliminarily test mechanistic retrieval algorithms for OACs in the Great Lakes.     

Beach science in the Great Lakes

Monitoring beach waters for human health has led to an increase and evolution of science in the Great Lakes, which includes microbiology, limnology, hydrology, meteorology, epidemiology, and metagenomics, among others. In recent years, concerns over the accuracy of water quality standards at protecting human health have led to a significant interest in understanding the risk associated with water contact in both freshwater and marine environments. Historically, surface waters have been monitored for fecal indicator bacteria (fecal coliforms, Escherichia coli, enterococci), but shortcomings of the analytical test (lengthy assay) have resulted in a re-focusing of scientific efforts to improve public health protection. Research has led to the discovery of widespread populations of fecal indicator bacteria present in natural habitats such as soils, beach sand, and stranded algae. Microbial source tracking has been used to identify the source of these bacteria and subsequently assess their impact on human health. As a result of many findings, attempts have been made to improve monitoring efficiency and efficacy with the use of empirical predictive models and molecular rapid tests. All along, beach managers have actively incorporated new findings into their monitoring programs. With the abundance of research conducted and information gained over the last 25 years, “Beach Science” has emerged, and the Great Lakes have been a focal point for much of the ground-breaking work. Here, we review the accumulated research on microbiological water quality of Great Lakes beaches and provide a historic context to the collaborative efforts that have advanced this emerging science.     

Mutagenicity of Great Lakes Sediments

The Ames/salmonella assay optimized for use with sediment extracts was used to assess the mutagenic potential of contaminated sediments collected from the Saginaw River, the Buffalo River, and Indiana Harbor as part of the Assessment and Remediation of Contaminated Sediments Program undertaken by the Great Lakes Program Office of the U.S. Environmental Protection Agency. Ames assays were conducted with 35 organic chemical extracts prepared from sediment samples collected from a total of 29 stations in the three areas of concern. Prior to the assay extracts required pre-treatment by gel permeation chromatography, but no further fractionation was performed. Mutagenicity was detected in both grab and core sediment samples from every station. Of the four bacterial strains tested, only TA98 consistently identified mutagenicity.     

Great Lakes Flood Thresholds and Impacts

Using the location, data, and water levels from flood events along the Canadian shore of the Great Lakes, flood damage thresholds were determined to identify and compare water levels at which static and storm-induced high water impact shoreline interests on several shore reaches of Lakes Erie, Huron, Ontario, and St. Clair. Spatial differences identified may be related to several factors, including: 1) nearshore bathymetries; 2) extent of residential development along low-lying shorelines; 3) degree of riparian adjustment to flooding; and 4) location relative to dominant wind or storm directions. Correlation analyses found that flood damage levels are more closely correlated to fluctuations in static levels on Lakes Ontario, Huron, and St. Clair, while flood damage levels are more closely correlated to maximum instantaneous water levels on Lake Erie. Correlation analyses of individual gauge data identified locations possibly more susceptible to storm surges. A conservative approach to determining flood damage thresholds is suggested, being based on a standard deviation below the mean of maximum instantaneous flood levels for a given gauge. The standard deviation threshold, while lower than current “critical levels” used in management, is more representative of the majority of flood damage levels than thresholds based on lowest maximum instantaneous lake levels. However, caution is urged in applying any critical level solely based on water level gauge information as Great Lakes flooding is a highly site-specific phenomenon influenced by meteorologic factors.     

Great Lakes Ice Thickness Prediction

Weekly ice thickness data, collected from 24 bay, harbor, and river sites on the Great Lakes, were correlated with freezing degree-day accumulations to develop regression equations between ice thickness and freezing degree-days. The data base at ice measurement sites was 3 to 8 winters in length. Ths standard error of estimate varied for individual regression equations and averaged between 7 and 8 cm for five forms of regression equations. Because the regression equations are empirical, the range of input data used to predict ice thickness should be limited to the range of values used in the derivation.     

Toxaphene trends in the Great Lakes fish

As part of the U.S. Great Lakes Fish Monitoring and Surveillance Program (GLFMSP), more than 300 lake trout (Salvelinus namaycush) and walleye (Stizostedion vitreum vitreum) collected from the Laurentian Great Lakes each year from 2004 to 2009, have been analyzed for total toxaphene and eight selected congeners. The analytical results show fish toxaphene concentrations are quite different among lakes. Between 2004 and 2009, Lake Superior lake trout had the highest concentration (119 to 482 ng/g) and Lake Erie walleye had the lowest concentration (18 to 47 ng/g). Combining these results with the historical total toxaphene data (1977–2003), temporal changes were examined for each lake. Because of different analytical methods used in the previous studies, the historical data were adjusted using a factor of 0.56 based on a previous inter-method comparison in our laboratory. Trend analysis using an exponential decay regression showed that toxaphene in Great Lakes fish exhibited a significant decrease in all of the lakes with t_1/2 (confidence interval) of 0.9 (0.8–1.1) years for Lake Erie walleye, 3.8 (3.5–4.1) years for Lake Huron lake trout, 5.6 (5.1–6.1) years for Lake Michigan lake trout, 7.5 (6.7–8.4) years for Lake Ontario lake trout and 10.1 (8.2–13.2) years for Lake Superior lake trout. Parlars 26, 50 and 62 were the dominant toxaphene congeners accounting for 0.53% to 41.7% of the total toxaphene concentration. Concentrations of these congeners generally also decreased over time.     

The flathead catfish invasion of the Great Lakes

A detailed review of historical literature and museum data revealed that flathead catfish were not historically native in the Great Lakes Basin, with the possible exception of a relict population in Lake Erie. The species has invaded Lake Erie, Lake St. Clair, Lake Huron, nearly all drainages in Michigan, and the Fox/Wolf and Milwaukee drainages in Wisconsin. They have not been collected from Lake Superior yet, and the temperature suitability of that lake is questionable. Flathead catfish have been stocked sparingly in the Great Lakes and is not the mechanism responsible for their spread. A stocking in 1968 in Ohio may be one exception to this. Dispersal resulted from both natural range expansions and unauthorized introductions. The invasion is ongoing, with the species invading both from the east and the west to meet in northern Lake Michigan. Much of this invasion has likely taken place since the 1990s. This species has been documented to have significant impacts on native fishes in other areas where it has been introduced; therefore, educating the public not to release them into new waters is important. Frequent monitoring of rivers and lakes for the presence of this species would detect new populations early so that management actions could be utilized on new populations if desired.     

Objective Wind Forecasting and Verification on the Great Lakes

The Techniques Development Laboratory of the National Weather Service has developed an automated objective wind forecast scheme. The forecasts are currently being transmitted twice daily for the five Great Lakes. Wind forecasts are made for 12 locations on the lakes by the Model Output Statistics technique. Mean absolute errors in wind speed, for the various forecast periods, range from 5 to 8 knots (2.6 to 4.1 m sec^?l). Mean absolute errors in direction are as low as 20 degrees for the short-term forecasts (6- to 12-hour periods) to as high as 70 degrees for the longer term forecasts (30 to 36 hours).     

Spectral Attenuation and Irradiance in the Laurentian Great Lakes

Optical data collected between 1973 and 1979 are utilized to study spectral attenuation and irradiance in the midlake waters of four Laurentian Great Lakes. Particular attention is given to the photosynthetic available radiation (PAR), its incident spectral distribution, its spectral attenuation, and its qualitative change with depth. Curves are shown illustrating these spectral properties as well as the relationships between PAR and the photosynthetic usable radiation (PUR) for each of the lakes. These curves, along with the included mathematical relationships, enable quantitative estimates to be obtained of incident PAR, subsurface PAR, and subsurface PUR, and qualitative information to be obtained on subsurface irradiance levels for the Laurentian Great Lakes.     

Algal-Available Particulate Phosphorus in the Great Lakes Basin

For the purpose of comparing the relative availability of particulate phosphorus (P) from various sources to the Great Lakes, algal-available P was determined on suspended solids and bottom sediments from tributaries, wastewater suspended solids, lake bottom sediments, and eroding bluff solids from the region. Physicochemical and bioassay methods were used to estimate the rate and extent of available P release from particulates. Considering all types of particulates examined, ultimately available P ranged from nil to approximately 70 percent of total phosphorus (Total-P) content. During algal bioassays, changes in levels of base-extractable inorganic P (R-NaOH-P) in tributary suspended solids were nearly equivalent to the amounts of P used by algae during bioassays. For the tributary solids, ultimately available P averaged approximately 90 percent of R-NAOH-P. Consistent differences were found in amounts of available P among particles from different sources. Sources of particle-bound P ranked in order of decreasing availability were: wastewater solids, lake bottom sediments, tributary solids, and eroding bluff solids. Differences in available P release rates also existed among the different types of particles. Wastewater solids displayed the largest first-order release rates, eroding bluff samples and tributary-suspended solid samples that were high in apatite showed essentially no available P release, while other tributary suspended solids displayed intermediate release rates.     

Stability Effects on Great Lakes Evaporation

The effects of atmospheric stability on Great Lakes evaporation computed by the modified mass transfer method have been evaluated by analysis of stability effects on the variable mass transfer coefficient, land to lake data adjustments, and ice-cover reduction of evaporation during winter. The Great Lakes which produce extreme results, Lakes Superior and Erie, and a much smaller water body within the Great Lakes chain, Lake St. Clair, were studied. Comparison of these evaporation estimates with previous studies, which excluded variable stability effects, shows that the previous studies of Lake Superior produced generally similar total annual water loss from the lake, but significantly overestimated both the seasonal high evaporation and the condensation rates. These tended to balance each other. The atmospheric conditions over Lakes Erie and St. Clair do not become as strongly stable and they normally do not exhibit large condensation. Previous evaporation studies for these lakes indicate generally higher evaporation rates, with significant overestimation of the total annual water losses (25%).     

Sustainable Groundwater Allocation in the Great Lakes Basin

Outdated groundwater allocation policies have resulted in unrestrained abstraction of groundwater in the Great Lakes Basin. Continuing on this course will lead to more frequent conflicts and further degradation of the Basin's ecosystem. Alternative approaches must focus on achieving sustainable groundwater allocation. The authors present two alternative institutions, local collaborative planning for groundwater allocation, and a regional watershed board. Collaborative institutions responsible for local groundwater planning should be established according to practical geographical units, have access to sound scientific information, utilize adaptive management and engage in open deliberation. The regional watershed board should establish a comprehensive and unified inventory of all groundwater resources in the Basin, designate critical groundwater areas, monitor groundwater management by respective jurisdictions, and make recommendations on best practices.     

Early Diagenesis of Mercury in the Laurentian Great Lakes

The early diagenesis of mercury in deep lake environments was investigated by examining the distribution of mercury among waters and sediments from several depositional basins in the Laurentian Great Lakes. Partitioning of mercury among different sediment phases was examined by sequential chemical extraction (using procedures specifically designed for mercury). Mercury in porewaters and sediment extracts was analyzed by flow-injection/hydride-generation atomic absorption spectroscopy.Results indicate that mercury is affected by early diagenesis at all of the sites studied. Much of the mercury is enriched in the surface layer of sediments, where it is primarily associated with organic matter and iron oxides. The redox cycling of iron and manganese influences the behavior of mercury; concentration profiles suggest that as oxides begin to dissolve in reduced sediments, nearly all of the adsorbed mercury is released. Organic matter decay also appears to release significant amounts of mercury. Porewater profiles suggest that most of the dissolved mercury released from decaying organic matter or from dissolving iron oxides may be taken up by freshly deposited organic matter and iron oxides in the near-surface layers. Much of the mercury that reaches the sediment column is thus recycled near the sediment-water interface, increasing both the residence time and the concentrations of mercury in surface sediments of these deep lake basins.